#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<math.h>
int main()
{
	int x1 = 0;
	int y1 = 0;
	int x2 = 0;
	int y2 = 0;
	float distance = 0;
	int num = 0;
	scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
	num = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
	distance = sqrt(num);
	printf("%.2f", distance);
	return 0;
}